PH-009 Digital pH Meter.  Measures pH range 0 to 14.  .1 pH resolution.  Comes with pH meter, protective plastic case, calibration screwdriver, battery and manual.

Use the pH meter to check the pH of your water, mash, [test Star San effectiveness] and finished beer.

Update: Since this post was published the price, availability or promotion has changed.  Check the product page for current description, price and availability.  Also: Today’s Deals on Amazon

New Mini Digital Pen Type PH Meter PH-009 I Multimeter Tester Hydro

Also: All Grain Tips & Gear | Star San Tips, Tricks and Guidelines